The present invention generally relates to a borehole telemetry system.
One of the more difficult problems associated with any borehole is to communicate measured data between one or more locations down a borehole and the surface, or between down-hole locations themselves. For example, communication is desired by the oil industry to retrieve, at the surface, data generated down-hole during operations such as perforating, fracturing, and drill stem or well testing; and during production operations such as reservoir evaluation testing, pressure and temperature monitoring. Communication is also desired to transmit intelligence from the surface to down-hole tools or instruments to effect, control or modify operations or parameters.
Accurate and reliable down-hole communication is particularly important when complex data comprising a set of measurements or instructions is to be communicated, i.e., when more than a single measurement or a simple trigger signal has to be communicated. For the transmission of complex data it is often desirable to communicate encoded digital signals.
One approach which has been widely considered for borehole communication is to use a direct wire connection between the surface and the down-hole location(s). Communication then can be made via electrical signal through the wire. While much effort has been spent on “wireline” communication, its inherent high telemetry rate is not always needed and very often does not justify its high cost.
Wireless communication systems have also been developed for purposes of communicating data between the surface of the well and a downhole tool. These techniques include, for example, communicating commands downhole via pressure pulses and fluid or acoustic communication, for example. A difficulty with some of these arrangements is that the communication is limited in scope and/or may require a relatively large amount of downhole power.
Thus, there is a continuing need for a borehole telemetry system that addresses one or more of the problems that are stated above as well as possibly addresses one or more problems that are not stated forth above.